Sandy Stier (left) and Kris Perry were one of two couples who sued to overturn Proposition 8, the 2008 state initiative that defined marriage as being between a man and a woman.

Photo: Lea Suzuki, The Chronicle

Sandy Stier (left) and Kris Perry were one of two couples who sued...

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Plaintiffs Jeff Zarillo (left) and Paul Katami (right) in front of the Phillip Burton Federal Building in San Francisco, Calif., as they arrive for Judge James Ware's hearing on the Proposition 8 proponents' motion to vacate Judge Walker's ruling holding Proposition 8 unconstitutional on Monday, June 13, 2011. Chad Griffin (background, right), Board President of the American Foundation for Equal Rights, is representing the plaintiffs in the Prop 8 lawsuit.

Photo: Liz Hafalia, The Chronicle

Plaintiffs Jeff Zarillo (left) and Paul Katami (right) in front of...

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Recently retired U.S. District Judge Vaughn Walker, author of rulings on same-sex marriage and wiretapping, sits with veteran members of the press in the Federal Building to discuss his plans for the future on Wednesday April 6, 2011 in San Francisco, Calif.

Photo: Mike Kepka, The Chronicle

Recently retired U.S. District Judge Vaughn Walker, author of...

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SAN FRANCISCO, CA - FEBRUARY 07: Same-sex couple Breana Hansen (L) and Monica Chacon kiss as they celebrate outside of San Francisco City Hall on February 7, 2012 in San Francisco, California. A three-judge panel of the 9th U.S. Circuit Court of Appeals ruled that the voter-approved Proposition 8 measure violates the civil rights of gay men and lesbians. (Photo by Justin Sullivan/Getty Images)

Photo: Justin Sullivan, Getty Images

SAN FRANCISCO, CA - FEBRUARY 07: Same-sex couple Breana Hansen (L)...

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Opponents of Proposition 8, a voter-approved ban on same-sex marriage, demonstrate outside the Ninth U.S. Circuit Court of Appeals in San Francisco, Feb. 7, 2012. A federal appeals court panel ruled Tuesday that the voter-approved ban in California violated the Constitution, all but ensuring that the case will proceed to the U.S. Supreme Court.

Photo: Jim Wilson, New York Times

Opponents of Proposition 8, a voter-approved ban on same-sex...

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Same-sex couple Frank Capley-Alfano (left) and Joe Capley-Alfano kiss as they celebrate outside of San Francisco City Hall on February 7, 2012 in San Francisco, California. A three-judge panel of the 9th U.S. Circuit Court of Appeals ruled that the voter-approved Proposition 8 measure violates the civil rights of gay men and lesbians.

Photo: Justin Sullivan, Getty Images

Same-sex couple Frank Capley-Alfano (left) and Joe Capley-Alfano...

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Thom Watson, (left) and Jeff Tabaco, a couple for eight years join same-sex couples and their families as they hold a , "No Standing for Prop 8" sit-in in front of the California State Building in San Francisco, Ca., on Tuesday September 6, 2011. Earlier a federal district court found that proposition 8's exclusion of loving, committed couples from marriage violated the fundamental fairness and equality guarantees of our constitution.

Among the arguments that supporters of same-sex marriage in California plan to make to the U.S. Supreme Court is that the sponsors of Proposition 8, the 2008 initiative that defined marriage as a male-female union, have no right to defend the state law in federal court.

It's an argument they might come to regret. If it succeeds, some legal analysts say the ruling may be so narrow that it benefits only the two couples who filed the suit, leaving Prop. 8 in effect for the rest of the state.

The uncertainty involves the concept of legal standing, the requirement that opposing sides in the case show they have something at stake so that the court is deciding an actual dispute and not just a theoretical argument.

The issue arose in the Prop. 8 case when the state attorney general - first Jerry Brown, then Kamala Harris - refused to defend the voter-approved state law, saying they considered it unconstitutional. When a federal judge declared Prop. 8 unconstitutional in 2010, the state agreed, leaving the fate of any appeal up to Protect Marriage, the conservative religious coalition that had put the measure on the ballot.

As private citizens, the coalition's members are unaccountable to the public and lack authority to enforce the law. But denying them standing would have left a voter-approved measure without a legal defense - as the California Supreme Court noted when it unanimously declared that Protect Marriage could represent the state's interests in an appeal.

The Ninth U.S. Circuit Court of Appeals adopted that recommendation before issuing its February 2012 ruling that also invalidated Prop. 8. But the nation's high court may have other ideas.

Court takes up issue

The justices have scheduled a hearing March 26 in the case and have asked both sides for arguments on the legal standing of Prop. 8's sponsors.

Coming from this court, the question has to be taken seriously. The conservative majority has narrowed access to the federal courts by denying standing to other litigants claiming intangible interests - for example, private citizens who object to White House funding for religious organizations.

If the justices deny standing to Protect Marriage, they would dismiss the group's appeal without deciding whether Prop. 8 was constitutional.

What would happen next is anyone's guess. But according to Martin Lederman, a Georgetown University law professor, former Justice Department lawyer in the Clinton and Obama administrations, and author of a series of essays on the Prop. 8 case on the Scotusblog website, gay-rights advocates would probably have nothing to celebrate.

First, the federal appeals court's decision striking down Prop. 8 would be set aside because it arose from an appeal by Protect Marriage.

That would leave the August 2010 ruling by Chief U.S. District Judge Vaughn Walker intact. Walker found Prop. 8 unconstitutional and issued an injunction prohibiting state officials from enforcing it - an order that appeared to legalize same-sex marriage statewide.

Lack of class action

But Lederman noted that the suit was not a class action on behalf of all same-sex couples in California. He said it appears to fall into the same category as another federal judge's 1992 order allowing an openly gay sailor to remain in the Navy - an order the judge framed as a nationwide injunction before the Ninth Circuit scaled it back to apply only to the sailor.

By the same standard, Lederman said, it's doubtful that Walker's order could be applied to anyone except the plaintiff couples, Kris Perry and Sandy Stier of Berkeley and Paul Katami and Jeff Zarrillo of Burbank.

At that point, Lederman said, Gov. Brown and Attorney General Harris, who have the sole authority to enforce Prop. 8, might decide it was no longer binding and order county clerks to issue marriage licenses to same-sex couples.

But any such decision would prompt more lawsuits. Court orders have kept Prop. 8 in effect while the case is on appeal.

Lederman's forecast last month didn't deter Prop. 8's challengers, lawyers for the two couples and the city of San Francisco. They plan to contest their opponents' legal standing, as well as the constitutionality of the ballot measure, in Supreme Court filings due Feb. 21, and reject suggestions that the argument could backfire.

A nonissue ... or not

"This is a nonissue," said Matthew McGill, a lawyer for the couples. Since Walker prohibited state officials from enforcing Prop. 8, and the state supports his ruling, McGill said, "there is nothing else to talk about. The state cannot enforce a law that it agrees is unconstitutional."

City Attorney Dennis Herrera said Walker's ruling would apply statewide because the couples' lawsuit, which San Francisco later joined, was a "facial challenge" of Prop. 8 - contesting its application to anyone, not just the four individuals.

That might not matter, said Joan Hollinger, a UC Berkeley law professor who also opposes Prop. 8 but finds Lederman's assessment plausible.

"I'm not convinced that federal rules would permit that generous construction of Walker's injunction," Hollinger said.

The same view cropped up in the Jan. 22 Supreme Court filing by lawyers for Protect Marriage.

While arguing that Protect Marriage had the right to represent California's voters and defend an initiative state officials have abandoned, the lawyers added that if the court disagrees, "the sweeping opinion and statewide injunction entered by (Walker) should be vacated."